The sniper who cops believe acted alone when he murdered six people in a two-day shooting spree in a Washington suburb laid low yesterday – as a police search found a matching bullet in the minivan of a Virginia woman wounded Friday, making her the attacker’s seventh victim.

There were no new shootings yesterday, and cops have yet to reel in a suspect in the random rampage that began Wednesday.

In the seventh shooting, a 43-year-old woman was struck in the lower back as she loaded packages into her minivan, but survived, cops said.

Montgomery County, Md., Police Chief Charles Moose said early yesterday he was hopeful forensic investigators would find identifiable bullets or bullet fragments in her vehicle linking her to the gunman. Later, sources told The Washington Post the bullet was found.

Police said the six slaughtered victims were each killed by a single .223-caliber bullet fired from long range with a high-powered rifle.

Cops initially wanted to question a North Carolina man with a possible connection to the marksman, but later ruled him out as having any knowledge of the shootings.

Montgomery County police said about 100 of its investigators were following up on about 600 credible tips.